Now: Will 2,4-D overcome its bad publicity?; Then: Reaction of weeds to 2,4-D

Issue date: Dec. 14, 1950. Initially developed for military use during the Second World War, 2,4-D was the first successful selective herbicide used to control broadleaf weeds in North America and its use by Canadian farmers was widespread within a few years of its commercial release in 1946.

NOW:

Last spring, the U.S. Department of Agriculture announced a postponement of its decision on whether to approve corn and soybean varieties that are tolerant of 2,4-D.

The department said it received more than 8,200 comments on the potential impact of this new technology. It also received petitions signed by more than 400,000 people, mostly opposing 2,4-D tolerant crops.

In comparison, 500 individuals and institutions submitted comments regarding the USDA’s review of corn and soybean varieties that tolerate dicamba.

Dean Riechers, a University of Illinois weed science professor, said the intense reaction to 2,4-D tolerance is mostly explained by hostility to genetically modified technology.

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Nonetheless, unfairly or not, Riechers said 2,4-D will always be linked to one of the most notorious chemicals in recent history — Agent Orange.

The U.S. military used the mixture of 2,4-D and 2,4,5-T as a defoliant during the Vietnam War to expose the location of enemy troops.

As noted on the American Cancer Society website, studies showed that 2,4,5-T caused birth defects in lab animals.

Subsequent studies on Vietnam veterans and lab tests suggested a link between Agent Orange and several types of cancer, including soft tissue sarcoma and Hodgkin’s disease, the society said.

Consequently, the Centre for Food Safety and other environmental organizations launched campaigns against corn with tolerance to 2,4-D, which they dubbed “Agent Orange Corn”.

Organizations such as Food & Water Watch have said 2,4-D tolerant corn could be dangerous “to eat because … 2,4-D is known to cause skin sores, liver damage and sometimes death in animals.”

Dow AgroSciences, which developed corn and soybean varieties that tolerate 2,4-D and glyphosate, has branded the technology as Enlist.

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In a 2012 statement, it said the U.S. Environmental Protection Agency has repeatedly reviewed the safety of 2,4-D and found it poses “a reasonable certainty of no harm.”

“EPA announced in 2004 that it had not found a link between 2,4-D and cancer, after a detailed 17-year evaluation, which included the input of third party health and safety experts,” Dow noted.

As well, the company said the health controversies surrounding Agent Orange are associated with a contaminant in 2,4,5-T, a herbicide that hasn’t been used for 25 years.

Given the intense focus on 2,4-D tolerant corn and soybeans, the upcoming USDA decision on this technology will be highly controversial.

Weed scientists have also criticized stacked herbicide tolerance, claiming it will only exacerbate the explosion of herbicide resistant weeds.

“It’s just another way of delaying the inevitable,” said Neil Harker, an Agriculture Canada weed scientist in Lethbridge.

“What you do by stacking technology is you get a reprieve for a few years and then (you) eventually select for multiple resistance.”

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Riechers said weeds will likely develop resistance to 2,4-D, but farmers have few options.

“There are fields (in the U.S. south) with Palmer Amaranth that flat out can’t be controlled anymore. The short-term solution is to mix glyphosate with either dicamba or 2,4-D,” he said.

“It’s not going to be a long-term fix because at some point the weeds will become resistant. But, in my opinion, if you do nothing there are going to be fields (with) Palmer Amaranth that prevent farmers from growing any crops on it.”

Riechers said 2,4-D will be around for decades because it remains an effective tool to kill troublesome weeds.

“I don’t think we’re going to burn it out and stop using it. The same with atrazine, 2,4-D and glyphosate. They still control a lot of weeds.”

The USDA is expected to decide on 2,4-D tolerant corn and soybeans in 2014.

Quebec and 2,4-D:

In 2006, laws came into effect in Quebec effectively banning the cosmetic use of 2,4-D. To justify the ban, the Quebec government said the herbicide was a possible carcinogen. In response, Dow AgroSciences, the manufacturer of 2,4-D, launched a lawsuit against Canada’s federal government, claiming Quebec’s ban wasn’t based on scientific evidence and contravened the North American Free Trade Agreement.

The case was settled in 2011, when Quebec agreed to a statement that “products containing 2,4-D do not pose an unacceptable risk to human health or the environment, provided that the instructions on their label are followed.”

Quebec continues to ban the cosmetic use of 2,4-D but the settlement may affect future bans or claims that 2,4-D causes cancer.

THEN: Reaction of weeds to 2,4-D

Issue date: Dec. 14, 1950. Initially developed for military use during the Second World War, 2,4-D was the first successful selective herbicide used to control broadleaf weeds in North America and its use by Canadian farmers was widespread within a few years of its commercial release in 1946.

Here is the latest information on the use of 2,4-D and other weed control chemicals, as compiled by the nation’s leading weed control experts at a recent meeting of the Western Canada Weed Control Conference at Regina. Kinds and amounts of chemical to be used on various types of weed, together with information on treatment of weeds in growing crops, have been set out here for the guidance of Western farmers.

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The Western Producer suggests you clip this column and check your 1951 weed control program against its recommendations.

Amounts 2,4-D Acid Per Acre

Suggested amounts of 2,4-D Acid per acre to use as a spray on cereals or flax to control weeds in Western Canada:

For Susceptible Annual Weeds — In cereals, use 3 1/2 to seven ounces of amine, or three to five ounces of ester acid per acre. In flax, use three to five ounces of amine, or 2 1/2 to four ounces of ester acid per acre.

For Intermediate Annual Weeds — In cereals, use five to 10 ounces of amine, or four to eight ounces of ester acid per acre. In flax, use four to eight ounces of amine, or three to six ounces of ester acid per acre.

For Perennial Weeds — (Top growth control). In cereals, use five to 10 ounces of amine, or four to eight ounces of ester acid per acre. In flax, use four to eight ounces of amine, or three to six ounces of ester acid per acre.

(Where 2,4-D is applied as a dust it is usually advisable to use from one to 1 1/2 ounces more acid per acre than recommended above.)

When to use 2,4-D in Growing Crops

Cereal Crops should be treated as soon as they have reached the three-leaf stage or when the leaves are six inches long. Grain may also be treated until the early shot-blade (boot) stage. Pre-harvest treatment can be done after the crop has passed the flowering stage.